The purpose of this study is to assess the efficacy of selumetinib in combination with docetaxel (75mg/m2) vs placebo in combination with docetaxel (75mg/m2) in patients with locally advance or metastatic NSCLCs that harbor mutations of KRAS. This study will also assess the PK, safety, patient reported outcomes (PRO) and tolerability profile of the selumetinib/docetaxel combination, compared to placebo in combination with docetaxel